Modified TM and TE waveguide modes and reflectivity by graphene layer in coupled-graphene-metal multilayer structure in sub-terahertz frequency

Abstract

In this paper we focus on the dispersion characteristics of TM and TE waveguide modes and the reflectivity of plane waves, incident on the four-layer structure consisting of air/graphene monolayer/dielectric buffer layer/metal substrate. The TM waveguide modes split up into two branches for small frequencies, one of the branches (cutoff waveguide branch) undergoes cutoff at a certain cutoff buffer thicknesses. There is no splitting of TE waveguide modes. However, these modes can be converted into short-range waves for smaller buffer thickness with subsequent modes cutoff depending on frequency and graphene electron concentration. Reflection coefficients of the TM polarized incident electromagnetic waves from air on the multi-layer structure vanish in the vicinity of cutoff buffer thicknesses. It is demonstrated that waveguide mode propagation constants and reflectivity in the multilayer structure can be considerably influenced by the presence of a graphene layer in the vicinity of the cutoff thicknesses of the waveguide modes.